Perovskite Solar Cells; Outshining Silicon
Snaith, Henry J.
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The cost of generating electricity from sun light using photovoltaic devices has continued to drop extensively over the last decade. Now in some locations in the world, PV generated electricity is cheaper than that from any other source. As the costs continue to drop and the efficiency of the PV modules continues to rise, the economic argument for globally widespread deployment of PV will become impossible to ignore. There have already been such advances in manufacturing the PV modules, that now the majority of the cost of a PV installation is the non-module costs, such as physical frames, electrical power handling, land and other soft costs. Therefore, from a PV technology perspective the most straight forward means to ensure the continuing drop in the cost of PV electricity is to enhance the efficiency of the modules. Current deployed PV is predominantly based on single-junction crystalline silicon. Most modules today are around 15 to 17% efficiency, with the more advanced “silicon technologies” promising modules of around 22%, but single junction silicon has a practical efficiency limit of around 25%. To move beyond this will require fundamentally superior technologies. Within the last few years organic-inorganic halide perovskites have risen to become a very promising PV material, captivating the research community, with the lab based cell efficiency rising form 4% to over 20% within a few years. In the most efficient devices, the perovskite semiconductor is present as a solid absorber layer sandwiched between negative (n) and positive (p)-type charge collection contacts. The perovskite itself is crystalized at low temperature by either, mixing precursor salts in a solvent and casting from solution, or via sublimation of the same salts under vacuum. Improving solar cell operation is reliant upon understanding and controlling thin-film crystallisation and controlling the nature of the p and n-type contacts. In addition, understanding and enhancing long term stability of the materials and devices if a key driver. One key advantage perovskites have over silicon is that the band gap (the lowest energy at which the material absorbs light) can be tuned broadly from around 1.2eV to 2.4eV. This enables the possibility of realising multi-junction solar cells, which could deliver much higher efficiency than single junction silicon, by either combining perovskites with silicon, or on their own. Snaith presents his work on developing thin film perovskite solar cells, introducing the technology and putting it into the broader perspective of the global PV industry. He discusses areas in which he has made recent advances and discuss the current status and potential for the “hybrid” perovskite-on-silicon tandem concept. He also presents broader applications where perovskite cells could find markets not currently met with crystalline silicon PV.